The underwater recovery of fluids from submerged tanks is becoming of considerable commercial importance. Discussion of a single recent incident in January 1997 in the Sea of Japan can emphasize this importance.
As of this date, the Russian Tanker "Nakhdka" sank off the Japanese coast in the Sea of Japan. The tanker broke into sections, with a large section sinking in 6,000 feet of water some 200 kilometers off the Japanese coast. As of the date of the filing of this patent application, oil continues to leak from this submerged hull section and drift ashore in Japan.
Environmental and commercial damage has followed in the wake of this accident. By way of example, it has been necessary to prevent the entry of oil into cooling water intakes of atomic power plants in Japan to prevent the oil from interfering with the required heat transfer.
From a review of the applicable prior art, it appears that the evacuation of oil from such submerged tanks has not been carefully and methodically considered before. Accordingly, in setting forth the problems to be overcome, I claim invention insofar as the prior art does not recognize the problems to be solved.
First, and assuming that oil is in a submerged tank, it is to be understood that the undersea pressures are considerable. For example, the ordinary pressure existing at around 6,000 feet of depth in the ocean is on the order of 3,000 pounds per square inch.
Second, it will be understood that conventional tanks--such as those found in tankers--are not designed to withstand pressure anywhere near the ambient pressure of the ocean at any depth. Accordingly, the first problem to be overcome is to equilibrate the pressure inside the tank being evacuated with the pressure outside the tank. Lacking such equilibration, tank collapse with oil discharge can occur.
Third, most oil transported in tankers is extremely viscous. With high viscosity, pumping from the tank site with a positive displacement pump taking a short suction on the tank is required. Thereafter, discharge from the tank to a surface vessel can occur.
Finally, conventional oil removal equipment should at all times be utilized. The utilization of specialized equipment should be held to an absolute minimum.